In machining, feedrate refers to the velocity at which the cutter tool is fed, that is, advanced against the workpiece. It may be desirable to set the tool at a certain feedrate, in order to achieve a desired machining result (e.g., to avoid damaging the workpiece). In order to control the feedrate, an approximation of the expected feedrate is typically calculated on a simulation of the machining. An accurate calculation of the feedrate may be crucial in high performance machining, for example in order to achieve a desired machined surface quality as well as to improve tool life and ultimately process economics.
Current methods of calculating the feedrate are approximations based on the tool center point displacement, tool tip displacement or spindle face center point. However, those methods typically are not sufficiently accurate to represent the relative speed between the tool and the workpiece.
The impact of inaccurate feedrate calculation typically varies between 5-axis point and flank machining styles.
FIG. 1 shows an example of 5-axis point machining style. In this example, the machining tool 100 is in contact with the machined surface 205 of the workpiece 200 at a contact point. The example figure defines the various points, namely the spindle center point (SCP) 105, the tool center point (TCP) 110 and the tool tip point (TTP) 115 which may be used to control the tool 100 and which may be basis of the calculated feedrate for programming the tool 100 (which may also be referred to as the programmed feedrate). Notably, the actual tool-workpiece contact point (TWCP) 120 may be different from each of SCP 105, TCP 110 and TTP 115, as the tool 100 travels over the machined surface 205 of the workpiece 200. The actual location of the contact point on the tool 100 typically varies depending on tool orientation, workpiece geometry and/or the relative location between the tool 100 and workpiece 200.
When feedrate cannot be calculated with sufficient accuracy, the operator typically must manually adjust the feedrate command values in the numerical control (NC) program before running the program, by relying on the operator's own experience, judgment and skills. This may require significantly slowing down the machining process, may require repeated trial-and-error, may be highly operator-dependent and/or may be a source of error.